1. Field of the Invention
This invention relates to water-in-oil latexes having water-soluble polymers dispersed therein, and more particularly, to specific compounds for promoting inversion of such latexes in water to disperse the polymers into the water. In one embodiment, the invention relates to water-in-oil latexes and inversion promoters that function to increase the viscosity of the water to a point significantly higher than the viscosity achieved by complete inversion of the latex and release of the polymer into the water alone.
2. Description of the Prior Art
Due to their thickening and flocculating properties, water-soluble polymers have been developed for use in many applications. For example, water-soluble polymers are used as mobility control agents in enhanced oil recovery operations such as water flooding. Water-soluble polymers can significantly increase the viscosity of aqueous media when dissolved therein.
A problem encountered in many applications of water-soluble polymers is dissolution of the polymers into water at a sufficient rate. It is known in the art that water-soluble polymers can be rapidly dissolved into water by preparing a water-in-oil latex (often referred to as an inverse latex) having the polymer dispersed in the water phase thereof, and inverting the latex into the water whereby the polymer is released into the water as a solution. Both the polymer and the latex can be conveniently formed at the same time by inverse emulsion polymerization techniques. Until the latex is inverted, the polymer remains in the dispersed water phase and does not significantly affect the viscosity of the latex allowing the latex to be easily handled and transported. Because the polymer is formed of small droplets and is already in solution, it easily disperses into the water upon inversion of the latex into the water.
Most latexes can be inverted by dilution with a large quantity of water. Inversion promoters and other means can be employed to facilitate and increase the rate of the inversion. Latex inversion promoters used heretofore include water-soluble surfactants having a high hydrophilic/lipophilic balance (HLB).
Over the past few years, very stable water-in-oil latexes have been developed for use in applications involving hostile environments such as oil field applications in the North Sea. The high electrolyte concentration of sea water and/or high temperature encountered in such applications preclude the use of conventional latexes. Examples of water-in-oil latexes of water soluble polymers suitable for use in hostile environments and methods for preparing such latexes are described in U.S. Pat. Nos. 4,906,701, 4,764,574 and 4,753,981 issued to Clark, Jr.
Unfortunately, due to their high stability, many water-in-oil latexes such as those described in U.S. Pat. Nos. 4,906,701, 4,764,574 and 4,753,981 are difficult to rapidly invert. In many oil field and other applications, inversion of the latex and release of the polymer into the water in a very short period of time (within minutes) is critical. Although conventional inversion promoters such as high HLB surfactants can be employed, they do not always decrease the inversion time sufficiently.